Disclosed herein are blends of polyetherimide and polyphenylene ether sulfone, methods for making the blends, and articles derived from such blends. The blends have a particularly advantageous combination of properties.
Blends of two or more polymers can have a single phase (miscible blends) or multiple phases (immiscible or phase separated blends). Phase separated blends are complex and unpredictable. These blends can demonstrate a host of behaviors from delamination to excellent impact strength, from opacity to transparency. The complexity and unpredictability of phase separated, multiphase polymer systems is such that small changes in composition or processing can have a dramatic effect on one or more physical properties. Overall, this makes it very difficult to achieve a desired combination of properties as modifications to the polymer system to address one physical property can cause significant changes in another property.
This is particularly true with regard to engineering thermoplastics, especially those with high glass transition temperatures such as polyetherimides. While polyetherimides have many valuable characteristics there is an increasing need for polymers or polymer blends with a combination of hydrolytic stability, high multiaxial impact energy, a high heat distortion temperature and a high modulus.
Concern about the spread of diseases, e.g., bovine spongiform encephalopathy, Creutzfeldt-Jakob disease and prions, has created heightened interest in high temperature sterilization. In the past, sterilization by use of devices such as an autoclave at 105° C. might have been acceptable. However, under new concerns, sterilization temperatures have been raised, in many instances to temperatures that can be as high as 130 to 138° C., or higher. These higher autoclaving and sterilization temperatures have placed added demands on plastic devices used in medical as well as food service and food preparation applications. Since many chemical reaction rates double for every 10° C. increase in temperature, the higher sterilization temperatures may cause chemical degradation, and ultimately, the breakage of plastic articles. Other plastics simply melt at the higher autoclave temperature. Thus, there is a need for plastic resins that will survive high temperature sterilization and autoclaving. In some applications, for example, in articles that will be used several times, retention of properties on exposure to repeated high temperature sterilization, as many as 100, 500 and even 1000 cycles of sterilization at 130 to 138° C., may be required. In some instances adjuvants, for example, morpholine or alkyl amines are added to the steam to prevent corrosion and protect the autoclave device and associated piping. Addition of these chemical bases to steam may further accelerate degradation of a thermoplastic resin placing even more performance demands on a suitable candidate resin.
In addition to resistance to autoclaving, such articles can also require other properties such as high impact to resist breakage in use. They also require heat resistance, in the form of a high heat distortion temperature to prevent melting or warping during sterilization. Additionally such articles will need high modulus and stiffness to give them the rigidly and strength for end use in devices such as trays, handles, bins, containers, animal cages, and connectors. In some instances having such devices that are transparent, so that the contents may be observed, is also useful.
For the foregoing reasons, there exists an unmet need for articles and compositions that have high impact strength, rigidity, resistance to deformation on exposure to heat, with the retention of properties upon repeated steam autoclaving at 130 to 138° C.